Author

Year of Award

Document Type

Degree Type

Degree Name

Geosciences

Department or School/College

Department of Geosciences

Committee Chair

Joel Harper

Keywords

climate, snowmelt, water resources, western Montana

Publisher

University of Montana

Abstract

The timing of mountain snowmelt is important for water resources in western Montana, where the majority of annual precipitation falls as snow. During the snowmelt season, the melting snowpack is subjected to a continuum of snow accumulation and/or sustained subfreezing temperature episodes that inhibit the generation and release of snowmelt. Snowmelt is delayed as heat transfer to the snowpack is reduced, but melt-runoff delays continue even after energy is again added to the snowpack. Following a storm episode, two energy barriers must be overcome before surface melt can drain through the snowpack: 1) cold content created by heat lost during the episode must be overcome, and 2) dry pore space must be filled with liquid water to residual saturation. We investigate the role of these two processes in delaying spring snowmelt following storm episodes in western Montana through analysis of ~10 years of historical snowpack and air temperature data for 33 stations in the Columbia River headwaters. The addition of pore space has a greater impact of delaying snowmelt than does the addition of cold content, with snow accumulation responsible for 86% of the collective energy deficit imposed on the snowpack during storm episodes. Combined influences from energy barriers imposed in the snowpack and atmospheric energy availability result in observed snowmelt delays averaging 4 days and occasionally reaching several weeks. Observed snowmelt delays due to spring storm episodes are comparable to shifts in historical snowmelt timing, and should be considered in studies on past and future snowmelt runoff.